Secure method for mtc device triggering

ABSTRACT

Upon receiving a triggering message from a MTC server (20), a network (10) verifies if the MTC server (20) is authorized to trigger a target MTC device (30) and also if the MTC device (30) is authorized to respond the triggering message, by comparing an MTC device ID and MTC server ID (and optionally information on subscription) which are include in the triggering message with authorized ones. Upon succeeding in the verification, the network (10) checks a trigger type included in the triggering message to verify if the triggering message is authorized to he sent to the MTC device (30). Upon succeeding in the check, the network (10) forwards the triggering message to the MTC device (30). The network (10) also validates a response from the MTC device (30), by checking whether the MTC device (30) is allowed to communicate with the addressed. MTC server (20).

TECHNICAL FIELD

The present invention relates to secure means forMachine-Type-Communication (MTC) device triggering, including securedelivery, of authorized MTC device triggering, failure handling such asretry of sending the triggering from network and MTC server to MTCdevice, and a method for triggering detached (or so-called offline) MTCdevice.

BACKGROUND ART

MTC device triggering is one of features defined by the Third.Generation Partnership Project's (3GPP's) Long Term Evolution-Advanced(LTE-A), as disclosed in Non Patent Literature (NPL) 1. The MTC devicetriggering is initiated by MTC server to network and terminated at MTCdevice. MTC server can be in or out of 3GPP network domain. A rouge MTCserver may send many MTC device triggering messages to overload thenetwork. Moreover, if MTC device responds to un-authorized triggering,it will cause battery consumption, sending of data towards the rouge MTCserver and potential mis-behaviour/mis-configuration of the MTC device.Therefore only valid triggering from authorized MTC server should besent to MTC device. Thus the MTC server should be able to establishsecurity association with the 3GPP network and MTC device to haveend-to-end security between them. On the other hand, it is also possiblethat rogue UEs (User Equipments) or MTC devices respond to triggering,this should he prevented by allowing only authorized devices to respondto triggering or developing solutions to check device authorization. Itis also possible that the MTC device triggering is not received by thetarget MTC device clue to issues like network failure. In order toreduce traffic, both the MTC server and the network should be able toresend the triggering.

CITATION LIST Non Patent Literature

-   [NPL 1] 3GPP TR 23.888, “System Improvements for Machine-Type    Communications; (Release 11)”, V1.4.0, 2011-August

SUMMARY OF INVENTION Technical Problem

Assume that the MTC server and the 3GPP network are mutuallyauthenticated. Now, based on the background art given above, the issuesto be solved are the following 1 to 7.

1. Network should he able to authorize messages from NTC server andvalidate the triggers. This is to prevent unauthorized behavior of MTCservers.

2. Network should be able to distinguish between different types oftriggers so that triggers are sent only to authorized MTC devices basedon their subscription.

3. Network congestion impact from trigger should be avoided.

4. MTC device should be able to validate trigger and its source so as toprevent attack or any impact on MTC device from unauthorized MTC serversand 2.0 messages.

5. Trigger freshness and lifetime solution should exist so as to preventreplay attack and network overload due to re-sending of trigger.

6. Trigger aggregation and security should be considered so as todecrease traffic in the network.

7. To avoid any other issues, the solution should be capable of takingcare of failure handling, which includes retry of sending the triggerand sending notification to MTC user.

Solution to Problem

An aspect of this invention considers MTC device triggering which isindicated by MTC server via the 3GPP network. The MTC server can be outof 3GPP network and only authorized triggering sent from identified andauthorized MTC server will he indicated to MTC device. In the same way,only authenticated and authorized MTC device will be allowed to respondto a valid triggering. Both network and MTC device will be able toauthorize the MTC server and the triggers from it.

The MTC server which is out of 3GPP network domain is required toestablish security association with MTC device even if securecommunication exists with the 3GPP network. The triggering content willbe protected and MTC device will he able to validate the trigger wherevalidation means being able to check: the message integrity, the sourceof trigger, whether replayed or not, that the message is within thelifetime and that the trigger is of the type to which the MTC deviceshould take action on. MTC device may deploy a list of authorized MTCservers, and MTC device can verify according to the list upon receivinga triggering. To prevent receiving maliciously sent triggers, networkwill be able to distinguish the trigger type.

The triggering message may have a lifetime such that it will not besimply copied and re-used by an attacker later. Upon network failure orotherwise, MTC server can resend the triggering message. Similarly,network can resend the MTC device within the trigger lifetime. Both MTCserver and network provide solutions that prevent trigger replay attack.

MTC device can be in detached status (or so-called offline) to saveenergy. Network can send MTC device a timer to attach in either DetachAccept or Detach Request towards MTC device, thus when the networkreceives MTC device triggering from MTC server, it can check thevalidity of the timer. If the timer is valid, network will hold thetriggering and wait till MTC device's attach, if not, network can sendthe triggering in the same way as MTC device is attached (or so-calledonline). The timer can be defined on subscription or can also becommunicated to the network by the MTC server.

Advantageous Effects of Invention

According to the present invention, the unnecessary network traffic canbe reduced and also the waste of battery consumption of MTC device canbe reduced, by preventing to send invalid triggering message.

Authorization of MTC server and MTC device according to the triggeringwill prevent invalid triggering message sent towards to MTC device,which can be from a rogue MTC server or a MTC server which is notauthorized to trigger the MTC device, or to a MTC device which is notauthorized to respond to the triggering.

One solution can be making MTC device perform periodic Attach Request tocheck if there is any triggering is sent to it. But this also results inunnecessary battery consumption and traffic. If the MTC server knowswhen it will trigger the MTC device, it can make the MTC device attachto network or staying idle, depends on the trigger frequency.

Securely retry of sending the triggering from network to MTC device willprevent interference with MTC server and any misuse of the triggeringmessage.

MTC device in detach (or offline) should not be always triggered as soonas the triggering message is received by the network. However, networkcan determine when to send the triggering message depends on theemergency status and invalidity of the timer for attach that networkallocated to MTC device.

Trigger is securely delivered to the MTC device by performingauthorization of MTC server, trigger message and also integrity andconfidentiality protection of the message.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration example of a systemaccording to a first exemplary embodiment of the present invention.

FIG. 2 is a sequence chart showing a first operation example in thesystem according to the first exemplary embodiment.

FIG. 3 is a sequence chart showing a second operation example in thesystem according to the first exemplary embodiment.

FIG. 4 is a sequence chart showing a third operation example in thesystem according to the first exemplary embodiment.

FIG. 5 is a block diagram showing a configuration example of a systemaccording to a second exemplary embodiment of the present invention.

FIG. 6 is a sequence chart showing a first operation example in thesystem according to the second exemplary embodiment.

FIG. 7 is a sequence chart showing a second operation example in thesystem according to the second exemplary embodiment.

FIG. 8 is a sequence chart showing a third operation example in thesystem according to the second exemplary embodiment.

FIG. 9 is a block diagram showing a configuration example of a nodeaccording to the exemplary embodiments.

FIG. 10 is a block diagram showing another configuration example of thenode according to the exemplary embodiments.

FIG. 11 is a block diagram showing a configuration example of an MTCserver according to the exemplary embodiments.

FIG. 12 is a block diagram showing a configuration example of an MTCdevice according to the exemplary embodiments.

DESCRIPTION OF EMBODIMENTS

Hereinafter, first and second exemplary embodiments of the presentinvention will be described.

First Exemplary Embodiment

As shown in FIG. 1, a system according to this exemplary embodimentincludes a 3GPP network 10, an MTC server 20, and a plurality of MTCdevices 30.

The inventors of this application have found that in such a system, forexample the following threats are identified for MTC device triggering.

<Threats>

The network triggers MTC devices to initiate communication with the MTCserver based on a trigger indication sent from the MTC server(hereinafter, this indication will be sometimes referred to as“triggering message”). This will open a chance for an attacker,especially when the MTC server is outside the operator domain as shownin FIG. 1.

The attacker can impersonate the MTC server to send a false triggerindication to the network, and then the network is utilized by theattacker to trigger the corresponding MTC device(s). This will causefalse decision on the MTC device which may lead to the waste of the MTCdevice's power consumption and even a DOS attack to the network, as alarge number of MTC devices are triggered and required authentication atthe same time. Thus the attackers can manipulate this to achieve theirattack target.

An authorized MTC server may not have full control over a MTC device, ifsuch MTC server inadvertently triggers a MTC device for e.g. updatingsoftware it can cause crucial damage to MTC device.

The attacker can eavesdrop privacy sensitive information such as MTCdevice identities on external interface.

In order to address these threats, especially when the MTC server islocated outside the 3GPP operator domain, the following securityrequirements apply.

<Security Requirements>

The 3GPP network should he able to determine whether (1) the MTC serveris authorized to communicate with the MTC device and (2) the MTC serveris authorized to send the given trigger to the given MTC device.

There are described solutions which fulfill these security requirementsfor the key issue.

<Solutions>

The 3GPP network should keep a list of MTC servers authorized to sendtrigger to a given MTC device and the type of trigger the MTC server isauthorized to send. The list should contain MTC device identity, MTCserver identity and the related allowed triggering. This way, for eachtrigger, the 3GPP network can verify if the MTC server is allowed tosend trigger and whether the trigger is authorized.

Next, there will he described details of this exemplary embodiment.

This exemplary embodiment caters for three main issues:

I. secure delivery of authorized MTC device triggering,

II. failure handling: retry of sending the triggering from network andMTC server to MTC device,

III. triggering detached (offline) MTC device.

A few assumptions are made as below.

1. MTC server is in/out of 3GPP domain network.

2. MTC device and network have mutual authentication.

3. MTC server and network have mutual authentication.

To achieve I (secure delivery of MTC device triggering), the triggermessage should be integrity and may be confidentiality protected. Thenetwork performs integrity and confidentiality checks of the trigger.

Network then performs authorization of MTC server. Network is deployedwith a list contains MTC device ID (identity), MTC server ID, andrelated information of subscription. MTC server will send the triggeringcontaining the target MTC device ID, MTC server 1D, and optionally thesubscription ID. When the network receives the triggering, it willperform authorization of MTC server according to the list, to verify ifthe MTC server is authorized to trigger the target MTC device and alsoif the MTC device is authorized to respond the triggering. Only when theauthorization for MTC server, MTC device and the subscription (in caseit appears) succeed, the network will proceed with MTC devicetriggering.

Network then performs authorization of the triggering message. Thetriggering message contains trigger type and trigger body. The triggertype consists of emergency level, subscription information andavailability of aggregation/broadcast trigger/group trigger, etc. Thetrigger body contains the expected behavior of MTC device, e.g., to sendback data, to update software, to attach to network, to detach fromnetwork, etc. The network checks the trigger type to verify if thetrigger message is authorized to be sent to MTC device. After successfultrigger type check, network will forward the trigger message to MTCdevice.

MTC device which receives the triggering indication (message) will alsoperform the integrity check and trigger type check to verify thevalidity of the trigger. Only after the validity is verified, the MTCdevice will respond to MTC server via network.

The network will also validate response from the MTC device to a MTCserver. Here the validation is to check whether the given MTC device isallowed to communicate with the addressed MTC server. Any unauthorizedor miscommunication will be informed to the user.

To achieve II (failure handling: retry of sending the triggering fromnetwork and MTC server to MTC device), when the trigger is failed to bedelivered to MTC device and MTC server is notified, MTC server can retryto send the trigger. It can also require the network to retry of sendingthe trigger to MTC device. The trigger has a lifetime and when it isexpired, the trigger should not be sent from MTC sever or network, andthe MTC device which receives a trigger with expired lifetime shoulddiscard the trigger. The trigger lifetime is synchronized between MTCserver and network. The frequency and upper limitation of how many timesthe trigger can be resent are defined and synchronized between MTCserver and network.

Network will start the retry after received it from MTC server. Oralternatively MTC server indicates network if retry of sendingtriggering message to MTC device is required.

Normally the network can resend the trigger to the MTC device until thelifetime of the trigger and the MTC server will resend the trigger tothe network after the lifetime of the trigger has ended.

In order to prevent replay attack, the receiver of the triggeringmessage should be able to distinguish if it is a retry message or anoriginal message. The triggering message should contain a parameterindicating its status (original or retry), and a counter of how manytimes it has been retried is defined in the retry messages.

Network sends a notification to MTC user if unauthorized triggeringmessage is received from an authorized MTC server. The notification canbe sent by any means, like SMS, email or recorded in a log. Any furtherunauthorized trigger should be discarded and if the MTC server keepssending the unauthorized triggers, network should suspend thecommunication with it.

To achieve III (triggering detached (offline) MTC device), offline MTCdevices are those that go to standby or sleep mode to save battery poweras they might not be required or have anything to communicate for agiven interval. This interval could be fixed in the sense that a MTCdevice wakes up periodically after the interval or it can be variable.For offline MTC device, it may not be necessary to be waken as soon asthere is a triggering from MTC server, or may have to wake upimmediately according to MTC server's requirement.

To determine when to send the trigger to MTC device, the network willfirst check the emergency level in the trigger type field. A triggerwith a high emergency level will be sent to MTC device immediately. Ifthe emergency level is low, the network will check if the offline timer(or time to attach) is valid, if not, the network will send the triggerimmediately. If the offline tinier is valid, the network will wait forattach request from MTC device, which is sent after the timer isexpired, before sending the trigger.

The time of attach is sent from network to MTC device, which can eitherbe in the Detach Accept or Detach Request message (other messages couldalso exist). This timer can be informed to the network from the MTCserver or agreed on at the time of subscription. Note that, the MTCdevice may inform the tinier to the network and the MTC server.

Unlike existing specification, a trigger can be sent to a MTC deviceeven when detached thus the security context to be used for suchemergency messages (or after offline timer expires) should he agreed onbefore the MTC device goes to detached state. The security context canbe indicated or negotiated during detach procedure (e.g., Detach Acceptor Detach Request message), so that MTC device can read the triggeringmessage and also protect future messages.

Next, operation examples of this exemplary embodiment will be describedin more detail with reference to FIGS. 2 to 4.

FIG. 2 shows an example of operations for the first issue of securedelivery of authorized MTC device trigger.

It is assumed that MTC device 30 and network 10 has mutualauthentication (Step S11). Further, it is assumed that network 10 andMTC server 20 has mutual authentication (Step S12).

Network 10 stores a list of authorized MTC server. The list contains MTCserver ID, ID of allowed target MTC device, subscription information,allowed trigger type to the MTC device (Step S13).

MTC server 20 sends a MTC device trigger to network 10 (Step S14).

Network 10 checks against the list to check whether the MTC server 20 isauthorized to send the trigger to given MTC device 30 and if MTC device30 is allowed to respond to the given type of trigger (Step S15). Forexample, the network 10 may verify that the MTC server 20 is allowed tosend the given type of trigger, if an ID of the MTC server 20 includedin the received trigger coincides with the MTC server ID included in thelist, and if the trigger type included in the trigger coincides with theallowed trigger type included in the list. Further, the network 10 mayverify that the MTC device 30 is allowed to respond to the trigger, ifan ID of the MTC device 30 included in the trigger coincides with theMTC device ID included in the list.

Network 10 forwards the trigger message to MTC device 30 if the checksat Step S15 are passed (Step S16).

When MTC device 30 receives the trigger message, it performs integritycheck and also checks the trigger type (Step S17).

MTC device 30 sends a proper response to network 10 (Step S18).

Network 10 checks against the list whether MTC device 30 is allowed torespond in the same way that. Step S15 does (Step S19).

Network 10 forwards the trigger response to MTC server 20 (Step S20).

FIG. 3 shows an example of operations for the second issue of failurehandling.

It is assumed that MTC device 30 and network 10 has mutualauthentication (Step S21). Further, it is assumed that network 10 andMTC server 20 has mutual authentication (Step S22).

MTC server 20 sends MTC device trigger message (Step S23). However, uponfailing in delivering the trigger message, either network 10 (Step S24)or MTC server 20 (Step S25) can check whether the trigger lifetime isexpired and/or retry counter is exceeded.

Specifically, network 10 checks whether the trigger lifetime is expiredand/or retry counter has reached the limit (Step S24 a). If none of StepS24 a happens, network 10 will forward the retry message of trigger toMTC device 30 (Step S24 b).

Alternatively, MTC server 20 performs the check as with the network 10(Step S25 a). If the check is passed, MTC server 20 retries sendingtrigger message to network 10 (Step S25 b). Network 10 forwards theretry trigger message (Step S25 c).

MTC device 30 verifies if the trigger is a retry message (Step S26).

When MTC device 30 received a retry trigger message which lifetime isexpired or retry counter is exceed, it will discard the trigger (StepS27).

FIG. 4 shows an example of operations for the third issue of triggeringoffline MTC device.

It is assumed that MTC device 30 and network 10 has mutualauthentication (Step S31). Further, it is assumed that network 10 andMTC server 20 has mutual authentication (Step S32).

During the detach procedure that MTC device 30 went offline (e.g. DetachRequest or Detach Accept message sent from network 10 to MTC device 30),network 10 sends MTC device 30 the re-attach timer and security contextindicator (Step S33 a). Alternatively, MTC device 30 can send there-attach timer to network 10 to inform when it will attach to network10 next time (Step S33 b).

MTC device 30 is offline (Step S34).

MTC server 20 sends a MTC device trigger message to the offline MTCdevice 30. The message contains the trigger type (Step S35).

Network 10 will check the trigger's emergency level (Step S36). If ithas high emergency level (Step S37), network 10 forwards the triggermessage immediately (Step S38).

If the trigger has low emergency level (Step S39), network 10 checks there-attach timer (Step S39 a). Network 10 waits for the re-Attach requestfrom MTC device 30 before the re-attach timer is expired (Step S39 b).Then, network 10 will forward the trigger message (Step S39 c).

Second Exemplary Embodiment

As shown in FIG. 5, in a system according to this exemplary embodiment,the network 10 includes a MTC-IWF (Inter-Working Function) 40. TheMTC-IWF 40 serves as a node relaying messages between the MTC device 30and an SCS (Service Capability Server) 60. The SCS 60 serves as the MTCserver 20 shown in FIG. 1. The network 10 includes, as other nodes, anHSS (Home Subscriber Server), an MME (Mobility Management Entity), anSGSN (Serving GPRS (General Packet Radio Service) Support Node), an MSC(Mobile Switching Centre) and the like. In the following description,the MME, SGSN and MSC are sometimes referred to as “MME/SGSN/MSC” andcollectively denoted by the symbol 50. Communication between the MTCdevice 30 and the MTC-IWF 40 is conducted through the MME/SGSN/MSC 50and a RAN (Radio Access Network). Note that, the MTC device 30 is a UE(User Equipment) equipped for MTC.

Next, operation examples of this exemplary embodiment will be describedin detail with reference to FIGS. 6 to 8.

FIG. 6 shows an example of operations for the first issue of securedelivery of authorized MTC device trigger.

It is assumed that MTC device 30 and MME/SGSN/MSC 50, MTC-IWF 40 hasmutual authentication (Step S41). Further, it is assumed that MTC-IWF 40and SCS 60 has mutual authentication (Step S42).

MTC-IWF 40 stores a list of authorized MTC server (SCS in this example).The list contains MTC server ID (SCS ID in this example), ID of allowedtarget MTC device, subscription information, allowed trigger type to theMTC device (Step S43).

SCS 60 sends a MTC device trigger to MTC-IWF 40 (Step S44).

MTC-IWF 40 checks against the list whether the SCS 60 is authorized tosend the given type of trigger to the target MTC device 30 and if MTCdevice 30 is allowed to respond to the given type of trigger from theSCS 60 (Step S45).

MTC-IWF 40 forwards the trigger message to MTC device 30 if the checksat Step S45 are passed (Step S46).

When MTC device 30 receives the trigger message, it performs integritycheck and also checks the trigger type (Step S47).

MTC device 30 sends a proper response to MTC-IWF 40 (Step S48).

MTC-IWF 40 checks whether MTC device 30 is allowed to respond (StepS49).

MTC-IWF 40 forwards the trigger response to SCS 60 (Step S50).

FIG. 7 shows an example of operations for the second issue of failurehandling.

It is assumed that MTC device 30 and MME/SGSN/MSC 50, MTC-IWF 40 hasmutual authentication (Step S51). Further, it is assumed that MTC-IWF 40and SCS 60 has mutual authentication (Step S52).

SCS 60 sends MTC device trigger message to MTC-IWF 40 (Step S53). Then,MTC-IWF 40 forwards the MTC device trigger message (Step S54). However,upon failing in delivering the trigger message, either MTC-IWF 40 (StepS55) or SCS 60 (Step S56) can check whether the trigger lifetime isexpired and/or retry counter is exceeded.

Specifically, MTC-IWF 40 checks whether the trigger lifetime is expiredand/or retry counter has reached the limit (Step S55 a). If none of StepS55 a happens, MTC-IWF 40 will forward the retry message of trigger toMTC device 30 (Step S55 b).

Alternatively, SCS 60 performs the check as with the MTC-IWF 40 (StepS56 a). If the check is passed, SCS 60 retries sending trigger messageto MTC-IWF 40 (Step S56 b). MTC-IWF 40 forwards the retry triggermessage (Step S56 c).

MTC device 30 verifies if the trigger is a retry message (Step S57).

When MTC device 30 received a retry trigger message which lifetime isexpired or retry counter is exceed, it will discard the trigger (StepS58).

FIG. 8 shows an example of operations for the third issue of triggeringoffline MTC device.

It is assumed that MTC device 30 and MME/SGSN/MSC 50, MTC-IWF 40 hasmutual authentication (Step S61). Further, it is assumed that MTC-IWF 40and SCS 60 has mutual authentication (Step S62).

During the detach procedure that MTC device 30 went offline (e.g. DetachRequest or Detach Accept message sent from network 10 to MTC device 30),MME/SGSN/MSC 50 sends MTC device 30 the re-attach timer and securitycontext indicator (Step S63 a). Alternatively, MTC device 30 can sendthe re-attach timer to MME/SGSN/MSC 50 to inform when it will attach tonetwork 10 next time (Step S63 b).

MTC device 30 is offline (Step S64).

MME/SGSN/MSC 50 sends the re-attach timer to the MTC-IWF 40 (Step S65).

SCS 60 sends a MTC device trigger message to the offline MTC device 30.The message contains the trigger type (Step S66).

MTC-IWF 40 will check the trigger's emergency level (Step S67). If ithas high emergency level (Step S68), MTC-IWF 40 forwards the triggermessage immediately (Step S68 a).

If the trigger has low emergency level (Step S69), MTC-IWF 40 checks there-attach timer (Step S69 a). If there is an Attach request from MTCdevice 30 before the re-attach timer is expired (Step S69 b), thenMTC-IWF 40 will forward the trigger message (Step S69 c).

Next, configuration examples of the MTC-IWF 40, the MME/SGSN/MSC 50, theMTC server 20 (SCS 60) and the MTC device 30 according toabove-mentioned exemplary embodiments will be subsequently describedwith reference to FIGS. 9 to 12.

As shown in FIG. 9, the MTC-IWF 40 includes a storing unit 41 and averifying unit 42 for the first issue of secure delivery of authorizedMTC device trigger. The storing unit 41 stores the list. The verifyingunit 42 verifies whether the MTC server 20 (SCS 60), the MTC device 30and the type of triggering message are authorized ones by checkingagainst the list. As substitutes for or in addition to the units 41 and42, the MTC-IWF 40 includes a checking unit 43 and a re-forwarding unit44 for the second issue of failure handling. The checking unit 43 checksthe trigger lifetime and/or the retry counter. The re-forwarding unit 44re-forwards the triggering message when the trigger lifetime is notexpired and/or the retry counter is not exceeded. As substitutes for orin addition to the units 41, 42 and 44, the MTC-IWF 40 includes thechecking unit 43 and a determining unit 45 for the third issue oftriggering offline MTC device. In this case, the checking unit 43 checksthe emergency level. The determining unit 45 determines a timing toforward the triggering message in accordance with the emergency level.Further, the MTC-IWF 40 may include an informing unit 46. The informingunit 46 informs the MTC device 30 of the re-attach tinier. Note that theunits 41 to 46 are mutually connected with each other thorough a bus orthe like. These units 41 to 46 can be configured by, for example,transceivers which respectively conduct communication with the MTCserver 20 and the MTC device 30, and a controller which controls thesetransceivers to execute the processes shown at Steps S11 to S16, S19 andS20 in FIG. 2, the processes shown at Step S21 to S25 in FIG. 3, theprocesses shown at Steps S31 to S39 in FIG. 4, the processes shown atSteps S41 to S46 and S48 to S50 in FIG. 6, the processes shown at StepsS51 to S56 in FIG. 7, the processes shown at Steps S61, S62 and S65 toS69 in FIG. 8, or processes equivalent thereto.

As shown in FIG. 10, the MME/SGSN/MSC 50 includes an instructing unit51. The instructing unit 51 instructs the MTC device 30 on the securitycontext. The unit 51 can be configured by, for example, transceiverswhich respectively conduct communication with the MTC device 30 and theMTC-IWF 40, and a controller which controls these transceivers toexecute the processes shown at Steps S63 and S65 in FIG. 8, or processesequivalent thereto.

Further, as shown in FIG. 11, the MTC server 20 (SCS 60) includes achecking unit 21 and a resending unit 22 for the second issue of failurehandling. The checking unit 21 checks the trigger lifetime and/or theretry counter. The resending unit 22 resends the triggering message whenthe trigger lifetime is not expired and/or the retry counter is notexceeded. As substitutes for or in addition to the units 21 and 22, theMTC server 20 includes an including unit 23 for the third issue oftriggering offline MTC device. The including unit 23 includes theemergency level in the triggering message. Note that the units 21 to 23are mutually connected with each other thorough a bus or the like. Theseunits 21 to 23 can be configured by, for example, a transceiver whichconducts communication with the MTC-IWF 40, and a controller whichcontrols this transceiver to execute the processes shown at Step S22,S23 and S25 in FIG. 3, the processes shown at Steps S32, S33 and S35 inFIG. 4, the processes shown at Steps S52, S53 and S56 in FIG. 7, theprocesses shown at Steps S6:2 and S66 in FIG. 8, or processes equivalentthereto.

Furthermore, as shown in FIG. 12, the MTC device 30 includes a checkingunit 31 and a sending unit 32 for the first issue of secure delivery ofauthorized MTC device trigger. The checking unit 31 performs theintegrity and trigger type check. The sending unit 32 sends the responseto the MTC-IWF 40 when the check is passed. As substitutes for or inaddition to the units 31 and 32, the MTC device 30 includes a discardingunit 33 for the second issue of failure handling. The discarding unit 33discards the triggering message when the trigger lifetime is expired orthe retry counter is exceeded. The MTC device 30 may include a verifyingunit 34. The verifying unit 34 verifies if the trigger message is theretry message by referring to the above-mentioned status (original orretry). As substitutes for or in addition to the units 31 to 34, the MTCdevice 30 includes an informing unit 35 for the third issue oftriggering offline MTC device. The informing unit 35 informs the MTC-IWF40 of the re-attach timer. Note that the units 31 to 35 are mutuallyconnected with each other thorough a bus or the like. These units 31 to35 can be configured by, for example, a transceiver which conductscommunication with the MTC-IWF 40, and a controller which controls thistransceiver to execute the processes shown at Steps S11 and S16 to S18in FIG. 2, the processes shown at Step S21 and S23 to S27 in FIG. 3, theprocesses shown at Steps S31, S33, S34 and S37 to S39 in FIG. 4, theprocesses shown at Steps S41 and S46 to S48 in FIG. 6, the processesshown at Steps S51 and S54 to S58 in FIG. 7, the processes shown atSteps S61, S63, S64, S68 and S69 in FIG. 8, or processes equivalentthereto.

Note that the present invention is not limited to the above-mentionedexemplary embodiments, and it is obvious that various modifications canbe made by those of ordinary skill in the art based on the recitation ofthe claims.

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2011-236699, filed on Oct. 28, 2011, thedisclosure of which is incorporated herein in its entirety by reference.

The whole or part of the exemplary embodiments disclosed above can bedescribed as, but not limited to, the following supplementary notes.

(Supplementary Note 1)

Validation of the Trigger at the Network:

Network performs authorization to both MTC server and the trigger toverify if the trigger is from an authorized MTC server and valid.

(Supplementary Note 2)

Validation of the trigger at the MTC device

MTC device verifies both if the trigger is from an authorized MTC serverand the validity of the trigger according to its subscription.

(Supplementary Note 3)

Validation of the message from MTC device to the MTC server at thenetwork

(Supplementary Note 4)

MTC server and network retry of sending the MTC device triggeringmessage upon e.g. network failure, meanwhile the trigger's freshness iskept.

(Supplementary Note 5)

Network notifies MTC user about receiving of unauthorized trigger andcan suspend further communication with the MTC server which sent thetrigger. The notification can be in any means like through SMS, email orbeing recorded in a log.

(Supplementary Note 6)

Network sends trigger to detached (offline) MTC device according toemergency level and timer for attach.

(Supplementary Note 7)

Network indicates the security context in the messages to be used in thenext communication.

REFERENCE SIGNS LIST

-   10 NETWORK.-   20 MTC SERVER-   21, 31, 43 CHECKING UNIT-   22 RECENDING UNIT-   23 INCLUDING UNIT-   30 MTC DEVICE-   32 SENDING UNIT-   33 DISCARDING UNIT-   34, 42 VERIFYING UNIT-   35, 46 INFORMING UNIT-   40 MTC-IWF-   41 STORING UNIT-   44 RE-FORWARDING UNIT-   45 DETERMINING UNIT-   50 MME/SGSN/MSC-   51 INSTRUCTING UNIT-   60 SCS

1.-52. (canceled)
 53. A SCS (Service Capability Server) in a mobilecommunication system, the SCS comprising: a transceiver configured tosend, to a MTC-IWF (Machine Type Communication-Inter Working Function),a trigger message including a time period for which the trigger messageis valid; and a controller configured to control the transceiver toperform mutual authentication between the MTC-IWF and the SCS, whereinthe trigger message is re-sent if a delivery of the trigger message to aUE (User Equipment) fails within the time period.
 54. A method of a SCS(Service Capability Server) in a mobile communication system, the methodcomprising: sending, to a MTC-IWF (Machine Type Communication-InterWorking Function), a trigger message including a time period for whichthe trigger message is valid; and performing mutual authenticationbetween the MTC-IWF and the SCS, wherein the trigger message is re-sentif a delivery of the trigger message to a UE (User Equipment) failswithin the time period.
 55. A MTC-IWF (Machine Type Communication-InterWorking Function) in a mobile communication system, the MTC-IWFcomprising: a transceiver configured to receive, from a SCS (ServiceCapability Server), a trigger message including a time period for whichthe trigger message is valid; and a controller configured to control thetransceiver to check whether the server is authorized to send thetrigger message, and to send the trigger message to a UE (UserEquipment) via a MME (Mobility Management Entity) or a SGSN (ServingGPRS Support Node), wherein the trigger message is re-sent if a deliveryof the trigger message to the UE fails within the time period.
 56. Amethod of a MTC-IWF (Machine Type Communication-Inter Working Function)in a mobile communication system, the method comprising: receiving, froma SCS (Service Capability Server), a trigger message including a timeperiod for which the trigger message is valid; checking whether theserver is authorized to send the trigger message; and sending thetrigger message to a UE (User Equipment) via a MME (Mobility ManagementEntity) or a SGSN (Serving GPRS Support Node), wherein the triggermessage is re-sent if a delivery of the trigger message to the UE failswithin the time period.
 57. A UE (User Equipment) in a mobilecommunication system, the UE comprising: a transceiver configured toreceive a trigger message from a MTC-IWF (Machine TypeCommunication-Inter Working Function) via a MME (Mobility ManagementEntity) or a SGSN (Serving GPRS Support Node); and a controllerconfigured to control the transceiver to send a trigger response to theMTC-IWF via the MME or the SGSN in response to the received triggermessage, wherein a SCS (Service Capability Server) sends, to theMTC-IWF, the trigger message including a time period for which thetrigger message is valid, and wherein the trigger message is re-sent ifa delivery of the trigger message to the UE fails within the timeperiod.
 58. A method of a UE (User Equipment) for a mobile communicationsystem, the method comprising: receiving a trigger message from aMTC-IWF (Machine Type Communication-Inter Working Function) via a MME(Mobility Management Entity) or a SGSN (Serving GPRS Support Node); andsending a trigger response to the MTC-IWF via the MME or the SGSN inresponse to the received trigger message, wherein a SCS (ServiceCapability Server) sends, to the MTC-IWF, the trigger message includinga time period for which the trigger message is valid, and wherein thetrigger message is re-sent if a delivery of the trigger message to theUE fails within the time period.
 59. The SCS of claim 53, wherein theMTC-IWF checks whether the SCS is authorized to send the triggermessage, and sends the trigger message to the UE via a MME (MobilityManagement Entity) or a SGSN (Serving GPRS Support Node).
 60. The methodof claim 54, wherein the MTC-IWF checks whether the SCS is authorized tosend the trigger message, and sends the trigger message to the UE via aMME (Mobility Management Entity) or a SGSN (Serving GPRS Support Node).61. The MTC-IWF of claim 55, wherein the trigger message includes anidentifier of the UE.
 62. The method of claim 56, wherein the triggermessage includes an identifier of the UE.
 63. The UE of claim 57,wherein the MTC-IWF checks whether the SCS is authorized to send thetrigger message.
 64. The method of claim 58, wherein the MTC-IWF checkswhether the SCS is authorized to send the trigger message.